1. Field of the Invention
The invention lies in the electronics field. Specifically, the invention pertains to a circuit configuration that can be employed either for a modulator, a demodulator, a down-converter, or else, for example, for an output amplifier.
2. Description of the Related Art
U.S. Pat. No. 5,530,929 to Lindqvist et al., which largely corresponds to published European patent application EP 0 643 494 A1, discloses a homodyne radio receiver. Such a receiver is illustrated in FIG. 1. A signal received by an antenna 12 is filtered through a bandpass filter 15. The bandpass filter 15 serves to select the correct communications band. An amplifier 16 is connected downstream of the bandpass filter 15. A high gain leads to high sensitivity and a low gain is desirable if a good dynamic range and a clean intermodulation characteristic are to be achieved. The output signal of the amplifier 16 is split into two signal components and fed to a respective mixer 11 and 11'. A local oscillator LO, which oscillates at a frequency fLo, is connected to a multiplier 13. The multiplier 13 multiplies the frequency fLo by a multiplication factor M (preferably M=3). The frequency M.multidot.fLo is subsequently divided by an integer factor N (preferably N=2). The signal generated as a result, having the frequency M: N.multidot.fLo, is fed to a phase shifter 19, which generates from this an in-phase signal (phase shift=0.degree.) and a quadrature signal (phase shift=90.degree.). These signals are additionally fed to the mixers 11 and 11'. The mixers 11 and 11' convert the radio-frequency input signal into an in-phase baseband signal I' and a quadrature baseband signal Q', respectively. The mixers 11 and 11' may be active or passive circuit elements. Low-pass filters 17 and 17' and amplifiers 18 and 18' are connected downstream of the mixers 11 and 11' in order to filter out and amplify the desired signal component. One disadvantage of that embodiment is that the local oscillator LO is not integrated in a chip.